1. Field of the Invention
This invention relates to strikes for doors, and in particular for electric strikes that are operable and can be changed to operate in fail-safe and fail-secure modes.
2. Description of the Related Art
Door locking mechanisms and security doors to prevent theft or vandalism have evolved over the years from simple doors with heavy duty locks to more sophisticated egress and access control devices. Hardware and systems for limiting and controlling egress and access through doors are generally utilized for theft-prevention or to establish a secured area into which (or from which) entry is limited. For example, retail stores use such secured doors in certain departments (such as, for example, the automotive department) which may not always be manned to prevent thieves from escaping through the door with valuable merchandise. In addition, industrial companies also use such secured exit doors to prevent pilferage of valuable equipment and merchandise.
Electric strikes are a class of door mechanisms that have been developed to control access to buildings or areas. An actuator (e.g. an electrically driven motor or solenoid) is used to move a blocking element to block or release a keeper to either prevent or allow release of a door's latch bolt. This keeps the door latched and in the locked position or allows the door to be opened. Typically, electric strikes have two modes, namely a “fail-secure” mode (where the door is locked with the power removed, i.e. the actuation means must be triggered to allow the door to be opened), and a “fail-safe” mode (where the door is unlocked with the power removed, i.e. the actuation means must be triggered to prevent the door from being opened). Some strikes on the market have only one-mode capability, while others are dual mode allowing the installer to select which mode is desired at the time of installation.
Different dual-mode electric strikes have been developed such as the commercially available GEM model GK-300 and ROFU 2400 series models. Each model has a solenoid mounted on a holder, which is movable within the strike housing. A blocking element is directly attached to the plunger of the solenoid, to block movement of the keeper when the strike is in its locked position. A first screw, reachable from outside the housing, cooperates with a slot or elongated opening in the housing, to define the path along which the holder is movable. The strike can be changed between fail-safe to fail-secure modes by loosening the first screw and moving it to one of the ends in the slot. The first screw can then be tightened to fasten the holder to the housing, i.e. the holder cannot move. First and second holes are arranged on the housing, to alternately align with a second screw, also reachable from outside the housing. At each end position along the holder path of movement one of a threaded third or fourth holes, both arranged on the holder, is aligned with either the first hole or the second hole, and the second screw can be inserted into the appropriate first or second hole and screwed into the visible third or fourth hole. This second screw arrangement helps hold the holder in its selected one of the end positions. The installer can configure the GEM and ROFU strikes in either the fail-safe or fail-secure mode by positioning the screw at one of the ends of the slot, and the second screw helps hold the strike in that mode. A similar arrangement is also reflected in U.S. Pat. No. 6,299,225 to Chang.
U.S. Pat. Nos. 6,874,830 and 7,144,053 to Bashford describe an electric strike having a housing, a keeper pivotally arranged in the housing, and a holder slidably arranged in the housing. The electric strike also includes a blocking element slidably arranged in the holder. The blocking element is configured to selectively prevent a rotation of the keeper and allow the rotation of the keeper. The electric strike also includes a two-position mode selector operable from outside the housing, and the selector is configured to selectively move the holder from a first position to a second position and vice versa. The electric strike also includes an actuator configured to selectively move the blocking element. Specifically, when the holder is in the first position, the blocking member allows the rotation of the keeper when the actuator is energized and prevents the rotation of the keeper when the actuator is not energized, and when the holder is in the second position, the blocking member prevents the rotation of the keeper when the actuator is energized and allows the rotation of the keeper when the actuator is not energized.
U.S. Pat. No. 7,540,542 to Geringer et al. describes an electric strike comprising a housing and a keeper pivotally mounted to the housing. A solenoid is arranged internal to the housing and movable between fail-safe and fail-secure positions. A two position mode control slot comprising two counter-bores is included in the housing and a mode control screw is included in the mode control slot. The screw is capable of being tightened in each of the two counter-bore positions in the control slot. The screw is changeable between the two of the positions without removal of the screw. The solenoid is in the fail-safe position when the screw is in one of the two positions and in the fail-secure position when the screw is in the other of the two positions.